For many years the changing of gear ratios in a mechanical device has been accomplished by disengaging the torque usually with a clutch.
Attempts have been made to force engagement with random selection, but this required a complete disengagement of the torque.
Different non-mechanical designs have been used for the purpose of changing the ratio with continuous torque. One is a double pulley arrangement that drives a V-belt, and constructed of metal elements. This is presently used in snowmobiles.
An other design uses rolling elements between an inner input and an outer output gear arranged much like an epicyclic gear train. The rolling elements can continuously change the gear ratio but they are torque-limited because they rely on the coefficient of static friction to transmit forces between the rolling elements.